1. Field of the Invention
The present invention relates to a process for the selective dimerization of isobutylene and especially to the use of C3 and/or C4 alkane as dimerization solvent together with the provision of tertiary butanol as a selectivity enhancing modifier during the dimerization.
2. Description of the Prior Art
The oligomerization of olefins such as isobutylene using acidic catalysts is a known reaction.
As described in U.S. Pat No. 3,760,026, a number of catalysts are known for this reaction including cold sulfuric acid, phosphoric acid on Kieselguhr, silica/alumina sometimes promoted with Ni, Co, Fe, Pt or Pd; activated natural clays plus activating substances such as ZnO metallic phosphates such as those of iron (III) and cerium optionally supported on carriers such as activated carbon, bauxite, activated carbon alone and with metal haliders such as TiCl2 heteropolyacids such as silicotungstic acid on silica gel and phosphomolybdic acid; BF3H3PO4 and BF3HPO3; dihydroxyfluroboric acid HF and fluorides or oxyfluorides of S, Se, N, P, Mo, Te, W, V and Si boiling below 300xc2x0 C.; BF3 dimethyl ether complexes; BF3 hydrocarbon complexes; BF3 SO2; and AlCl3 with cocatalysts such as dimethyl ether, HCl, and nitromethane. These catalysts and dimerization processes, including operating conditions, are known in the art.
An especially preferred catalyst is a sulfonic acid-type ion exchange resin such as Amberlyst A-15. U.S. Pat. No. 4,447,668 describes isobutylene dimerization using A-15 with methyl t-butyl ether as solvent.
Our U.S. Pat. No. 5,877,372 describes the selective dimerization of isobutylene using a sulfonic acid resin catalyst, tertiary butanol selectivity enhancing modifier and isooctane diluent.
U.S. Pat. No. 4,100,220 describes isobutylene dimerization using a sulfonic acid resin catalyst and tertiary butanol selectivity enhancing modifier. Minor amounts of butanes are shown in the dimerization feed.
Considerations associated with the isobutylene dimerization involve removal of the substantial heat of reaction and the requirement that high selectivity to the dimer product be maintained. The instant invention provides a process wherein these objectives are achieved.
In accordance with the present invention, a process is provided for the dimerization of isobutylene in the presence of both a selectivity enhancing amount of tertiary butanol and in the presence of C3 and/or C4, preferably C4 alkane as diluent. In an especially preferred practice, tertiary butanol such as that derived from the Oxirane propylene oxide/tertiary butanol process is used as starting material and isooctane formed by hydrogenation of dimer is the ultimate product.
The accompanying drawing is a schematic representation of an especially preferred practice of the invention.